The endocrine pancreas, composed of the islets of Langerhans, is responsible for the maintenance of blood glucose homeostasis. Several cell types comprise the islets and include glucagon-producing . cells, insulin- producing cells, somatostatin-producing d cells, pancreatic polypeptide-producing PP cells, and ghrelin- producing e cells. Diabetes mellitus is associated with a loss of insulin-producing cells. Current medical treatment is focused on management of blood glucose levels through insulin replacement as well as oral medications that facilitate insulin release, inhibit gluconeogenesis, and inhibit glycogenolysis. However, in 2000, it was determined that islets can be successfully transplanted into diabetic patients using cadaveric islets. Although cell replacement therapies have been successful, the paucity of donor islets has limited its application and has led to the need to create islets in the laboratory using stem cell technologies. Current stem cell differentiation protocols have been adapted and improved in response to studies of normal mouse pancreas development, however complete cell differentiation has yet to be achieved. Thus, continued investigation into normal pancreas development will be of utmost importance for creating better in vitro cell differentiation protocols for the generation of transplantable cells. Nkx2.2 is a homeodomain transcription factor that is essential for the production of several islet cell types. Nkx2.2 null mice do not form cells and have reduced numbers of a and PP cells. Instead, the Nkx2.2 null islets are filled with ghrelin cells, the predominant mono-hormonal islet cell population that forms in the ES cell differentiation protocols. Therefore, knowledge of Nkx2.2 function and regulation will be important for the development of proper islet cell differentiation protocols. Studies from the Sussel lab have indicated that Nkx2.2 functions as an activator and a repressor at different developmental time points and in different cellular contexts. At this time, the functional structure of the Nkx2.2 protein is not well characterized, although three domains have been described, including the DNA binding homeodomain, the groucho co-repressor interaction domain (TN) and the NK2-specific domain (NK2-SD), which is highly conserved amongst family members and across species, but its function is unknown. Despite its high homology, the function of the NK2-SD domain is unknown. Characterization of the function of the NK2- SD domain during pancreas development will facilitate the development of optimized cell differentiation protocols. Specific aims: 1. To determine whether the highly conserved Nkx2.2 NK2-SD domain mediates Nkx2.2 function in vivo, I will investigate the phenotypic changes associated with Nkx2.2NK2-SD mutant mice during embryonic development and in postnatal animals. 2. To understand the mechanism by which the NK2-SD domain influences Nkx2.2 mediated transcriptional regulation, I will characterize the DNA binding and transcriptional activities of the NK2-SD domain on candidate Nkx2.2 target promoters.